JP6953826B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

In the transfer of the toner image to the paper in the electrophotographic process, it is common to apply a bias between the image carrier or the intermediate transfer body and the paper to transfer the toner by electrostatic force. It is known that the strength of the electric field acting on the toner is affected by the electrical properties of the paper such as capacitance and electrical resistance.

In order to adjust the transfer bias according to the difference in paper, a method of setting the transfer bias according to the paper information (type, basis weight, etc.) set by the user has been put into practical use. Further, in recent years, in order to improve user convenience, a method of mounting a sensor for detecting the physical characteristics of paper and setting a transfer bias according to the detection information has been put into practical use.

However, these methods have the following problems. Paper information such as basis weight set by the user is related to some extent to the electrical properties of the paper that affect transfer, but it is not directly related to dielectric constant or resistance, so it may not be possible to set an appropriate transfer bias. In addition, since the user may not be able to determine the paper information or may not set it, it may not be possible to set an appropriate transfer bias.

When a sensor that detects the physical characteristics of paper is used, the cost for detecting it is higher than before, and a space for installing the sensor is required.

In response to the above problems, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-287966 (Patent Document 1), the electric resistance or capacitance of the paper is estimated by using the transfer current.

Further, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-276668 (Patent Document 2), the electric resistance or capacitance of the paper is estimated by using the static eliminating current.

Japanese Unexamined Patent Publication No. 2003-287966 Japanese Unexamined Patent Publication No. 2010-276668

However, in the image forming apparatus disclosed in Patent Document 1, even if the current is low only by the transfer current, the paper resistance is high and the current does not flow, or the capacitance of the paper is low and the current does not flow. I can't separate the current.

Further, in the image forming apparatus disclosed in Patent Document 2, the applied voltage is determined from the static elimination current detected by holding a table for each selected paper type (plain paper / thick paper, etc.) and humidity. However, since the static elimination current is affected by the secondary transfer current, the secondary transfer current changes depending on the paper type in the constant voltage control generally used in the secondary transfer. As a result, the static elimination current also changes. Therefore, depending on the paper type, it may not be possible to set an appropriate voltage on the prepared table.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of accurately setting transfer conditions when transferring a toner image to a recording medium. There is.

The image forming apparatus based on the present invention includes a first electrode portion including a contact electrode in contact with the conveyed recording medium and a counter electrode arranged to face the contact electrode so as to sandwich the conveyed recording medium. The contact electrode is arranged in a non-contact manner with respect to the recording medium so that the electric charge charged in the recording medium can move, and the recording medium is sandwiched between the contact electrode and the counter electrode. A first detection unit that detects the first current flowing through the first electrode portion by applying a voltage between the counter electrodes, and a second detection unit that detects the second current flowing from the charged recording medium to the second electrode portion. 2 The detection unit includes a first detection unit and a control unit for inputting the detection results of the second detection unit. The control unit sets transfer conditions for transferring the toner image to the recording medium using the first current detected by the first detection unit and the second current detected by the second detection unit. ..

In the image forming apparatus based on the present invention, the control unit estimates the electrical resistance and capacitance of the recording medium using the detected first current and the detected second current. It is preferable to set the transfer conditions based on the estimated electrical resistance and capacitance of the recording medium.

In the image forming apparatus based on the present invention, it is preferable that the first electrode portion is composed of a transfer apparatus that transfers the toner image carried on the toner image carrier to a recording medium.

In the image forming apparatus based on the present invention, it is preferable that the second electrode portion is composed of a static elimination electrode that eliminates the electric charge charged in the recording medium.

In the image forming apparatus based on the present invention, it is preferable that the second electrode portion is arranged on the downstream side of the first electrode portion in the transport direction of the recording medium.

In the image forming apparatus based on the present invention, the relationship between the electric resistance of the recording medium and the second current is such that the horizontal axis is the electric resistance of the recording medium and the vertical axis is the second current. The distribution of electrical resistance of the recording medium may be represented by a convex shape having a peak. In this case, when the detected second current is a value located in the region before and after the peak, the control unit applies a different voltage between the contact electrode and the counter electrode. Using the first current detected by the first detection unit and the second current that flows from the recording medium to the second electrode unit after applying a different voltage and is detected by the second detection unit, It is preferable to set the above transfer conditions.

In the image forming apparatus based on the present invention, the second detection unit detects when the higher voltage of the different voltages applied between the contact electrode and the counter electrode is applied. An abnormality is notified when the second current is not larger than the second current detected by the second detection unit when the lower voltage of the different voltages applied to the first electrode unit is applied. A notification unit may be further provided.

In the image forming apparatus based on the present invention, the control unit either stops the image forming process when an abnormality is notified by the notification unit, or the first detection unit detects the abnormality. It is preferable to set the above transfer conditions using only the electric current.

In the image forming apparatus based on the present invention, when the control unit prints on the first recording medium or the first recording medium after changing the type of the recording medium, the control unit described above. It is preferable to set the transfer conditions using the first current detected by the first detection unit and the second current detected by the second detection unit.

In the image forming apparatus based on the present invention, the control unit does not form an image on the first recording medium or the first recording medium after changing the type of the recording medium. The transfer condition may be set by using the first current detected by the first detection unit and the second current detected by the second detection unit during transportation.

In the image forming apparatus based on the present invention, the control unit estimates the electrical resistance and capacitance of the recording medium using the detected first current and the detected second current. Is preferable. In this case, the control unit increases the transfer voltage applied to the transfer device when transferring the toner image from the toner image carrier to the recording medium when the estimated electrical resistance of the recording medium is large, and the recording medium. When the capacitance of the above is large, it is preferable to reduce the transfer voltage.

The image forming apparatus based on the present invention may further include a cooling device that cools the recording medium after the toner image transferred to the recording medium is fixed. In this case, the control unit sets the cooling conditions of the cooling device using the first current detected by the first detection unit and the second current detected by the second detection unit. It is preferable to do so.

In the image forming apparatus based on the present invention, it is preferable that the control unit estimates the electric resistance of the recording medium by using the detected first current and the detected second current. In this case, it is preferable that the control unit increases the amount of heat absorbed from the recording medium by the cooling device when the estimated electrical resistance of the recording medium is large.

According to the present invention, it is possible to provide an image forming apparatus capable of accurately setting transfer conditions when transferring a toner image to a recording medium.

It is the schematic of the image forming apparatus which concerns on embodiment. It is the schematic which shows the peripheral structure of the secondary transfer apparatus which concerns on embodiment. It is a figure which shows the relationship between the secondary transfer current flowing through the secondary transfer apparatus which concerns on embodiment, and the electrical resistance of a paper. In the relationship shown in FIG. 3, it is a figure which shows an example of the thickness of the paper and the electric resistance of the paper when the secondary transfer current becomes 145 μA. It is the schematic which shows the peripheral structure of the static elimination electrode which concerns on embodiment. It is a figure which shows the relationship between the static elimination current flowing through the static elimination electrode which concerns on embodiment, and the electric resistance of a paper. It is a figure which shows an example of the thickness of a paper and the electric resistance of a paper specified from a secondary transfer current and a static elimination current. It is a figure which shows an example of the table used when calculating the physical characteristic of a paper in the image forming apparatus which concerns on embodiment. It is the schematic which shows the 1st state of the cooling apparatus which concerns on embodiment. It is the schematic which shows the 2nd state of the cooling apparatus which concerns on embodiment. An example of paper physical properties calculated from the secondary transfer current and static elimination current measured by the first detection unit and the second detection unit according to the embodiment, and transfer conditions and cooling conditions determined from the physical characteristics of the paper. It is a figure which shows. It is a figure which shows the 1st example of the flow which determines the transfer condition in the image forming apparatus which concerns on embodiment. It is a figure which shows the 2nd example of the flow which determines the transfer condition in the image forming apparatus which concerns on embodiment. It is a figure which shows the 3rd example of the flow which determines the transfer condition and the cooling condition in the image forming apparatus which concerns on embodiment. From the secondary transfer current and static elimination current detected by the first detection unit and the second detection unit according to the embodiment, and the detected secondary transfer current and static elimination current, the physical characteristics, transfer conditions, and cooling conditions of the paper are determined. It is a figure which shows an example of the table used at the time of determination. It is a figure which shows the 4th example of the flow which determines the transfer condition and the cooling condition in the image forming apparatus which concerns on embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments shown below, the same or common parts are designated by the same reference numerals in the drawings, and the description thereof will not be repeated.

FIG. 1 is a schematic view of an image forming apparatus according to an embodiment. The image forming apparatus 100 will be described with reference to FIG.

FIG. 1 shows an image forming apparatus 100 as a color printer. Hereinafter, the image forming apparatus 100 as a color printer will be described, but the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be a monochrome printer, a fax machine, or a monochrome printer, a color printer, and a multi-function peripheral (MFP).

The image forming apparatus 100 includes an image forming unit 1Y, 1M, 1C, 1K, an intermediate transfer belt 30, a primary transfer roller 31, a secondary transfer roller 33, a cassette 37, a driven roller 38, and a drive roller 39. A timing roller 40, a fixing device 50, a cooling device 80, a housing 90, and a control unit 101 are provided. The secondary transfer roller 33 and the drive roller 39 function as the secondary transfer device 61.

Further, the image forming apparatus 100 includes a secondary transfer device 61 as a first electrode unit, a static elimination electrode 62 as a second electrode unit, a first detection unit 71, and a second detection unit 72.

The secondary transfer device 61 is installed so as to sandwich the recorded recording medium to be conveyed, and is configured so that a voltage can be applied. The static elimination electrode 62 is arranged in a non-contact manner with respect to the recording medium so that the charged charge can be moved. The static elimination electrode 62 is arranged on the downstream side of the secondary transfer device 61 in the transport direction of the recording medium.

The first detection unit 71 detects the first current flowing through the secondary transfer device 61. The second detection unit 72 detects the second current flowing from the recording medium to the static elimination electrode 62. The first detection unit 71 and the second detection unit 72 are composed of, for example, a current sensor. The detection results by the first detection unit 71 and the second detection unit 72 are input to the control unit 101.

By the image forming unit 1Y, 1M, 1C, 1K, the intermediate transfer belt 30, the primary transfer roller 31, the secondary transfer roller 33, the cassette 37, the driven roller 38, the drive roller 39, and the timing roller 40. An image forming unit is configured. This image forming unit forms a toner image on the paper S as a recording medium which is conveyed along the conveying path 41 described later.

The image forming units 1Y, 1M, 1C, and 1K are arranged in order along the intermediate transfer belt 30. The image forming unit 1Y receives the toner supply from the toner bottle 15Y and forms a yellow (Y) toner image. The image forming unit 1M receives the toner supply from the toner bottle 15M and forms a toner image of magenta (M). The image forming unit 1C receives the toner supply from the toner bottle 15C and forms a toner image of cyan (C). The image forming unit 1K receives the toner supply from the toner bottle 15K and forms a black (BK) toner image.

The image forming units 1Y, 1M, 1C, and 1K are arranged along the intermediate transfer belt 30 in the order of rotation of the intermediate transfer belt 30, respectively. The image forming units 1Y, 1M, 1C, and 1K each include a photoconductor 10, a charging device 11, an exposure device 12, a developing device 13, and a cleaning device 17, respectively.

The charging device 11 uniformly charges the surface of the photoconductor 10. The exposure apparatus 12 irradiates the photoconductor 10 with laser light in response to a control signal from the control unit 101, and exposes the surface of the photoconductor 10 according to the input image pattern. As a result, an electrostatic latent image corresponding to the input image is formed on the photoconductor 10.

The developing device 13 applies a developing bias to the developing roller 14 while rotating the developing roller 14 to adhere toner to the surface of the developing roller 14. As a result, the toner is transferred from the developing roller 14 to the photoconductor 10, and the toner image corresponding to the electrostatic latent image is developed on the surface of the photoconductor 10.

The photoconductor 10 and the intermediate transfer belt 30 are in contact with each other at a portion where the primary transfer roller 31 is provided. The primary transfer roller 31 has a roller shape and is configured to be rotatable. By applying a transfer voltage having the opposite polarity to the toner image to the primary transfer roller 31, the toner image is transferred from the photoconductor 10 to the intermediate transfer belt 30. The yellow (Y) toner image, the magenta (M) toner image, the cyan (C) toner image, and the black (BK) toner image are superimposed in this order and transferred from the photoconductor 10 to the intermediate transfer belt 30. As a result, a color toner image is formed on the intermediate transfer belt 30.

The intermediate transfer belt 30 is stretched on the driven roller 38 and the driving roller 39. The drive roller 39 is rotationally driven by, for example, a motor (not shown). The intermediate transfer belt 30 and the driven roller 38 rotate in conjunction with the drive roller 39. As a result, the toner image on the intermediate transfer belt 30 is conveyed toward the secondary transfer roller 33 side.

The cleaning device 17 is pressure-contacted with the photoconductor 10. The cleaning device 17 collects the toner remaining on the surface of the photoconductor 10 after the transfer of the toner image.

Paper S is set in the cassette 37. The paper S is fed from the cassette 37 one by one to the secondary transfer roller 33 along the transport path 41 by the timing roller 40. The secondary transfer roller 33 has a roller shape and is configured to be rotatable. The secondary transfer roller 33 applies a transfer voltage having a polarity opposite to that of the toner image to the paper S being conveyed.

As a result, the toner image is attracted from the intermediate transfer belt 30 to the secondary transfer roller 33 side, and the toner image on the intermediate transfer belt 30 is transferred to the paper S. The transfer timing of the paper S to the secondary transfer roller 33 is adjusted by the timing roller 40 according to the position of the toner image on the intermediate transfer belt 30. The timing roller 40 transfers the toner image on the intermediate transfer belt 30 to an appropriate position on the paper S.

When a voltage is applied between the drive roller 39 and the secondary transfer roller 33 when the toner image is transferred to the paper S in this way, the drive roller 39 is passed through the paper S from the secondary transfer roller 33 side. The first current flows toward. This first current is detected by the first detection unit 71.

Further, during the secondary transfer, electric charges are accumulated on the paper S. The electric charge accumulated in the paper S moves toward the second electrode arranged close to the paper S when being transported along the transport path. As a result, a second current flows through the static elimination electrode 62. This second current is detected by the second detection unit 72.

The control unit 101 uses the first current detected by the first detection unit 71 and the second current detected by the second detection unit 72 to set transfer conditions for transferring the toner image to the paper S.

The fixing device 50 pressurizes and heats the paper S passing through itself. As a result, the toner image is fixed on the paper S. In this way, the fixing device 50 fixes the toner image on the paper S transported along the transport path 41. The paper S on which the toner image is fixed is discharged to the tray 48.

Although the image forming apparatus 100 that employs the tandem method as the printing method has been described above, the printing method of the image forming apparatus 100 is not limited to the tandem method. The arrangement of each configuration in the image forming apparatus 100 can be appropriately changed according to the printing method adopted. As the printing method of the image forming apparatus 100, a rotary method or a direct transfer method may be adopted. In the case of the rotary system, the image forming apparatus 100 is composed of one photoconductor 10 and a plurality of developing apparatus 13 rotatably configured on the same axis. At the time of printing, the image forming apparatus 100 guides each developing apparatus 13 to the photoconductor 10 in order to develop a toner image of each color. In the case of the direct transfer method, the image forming apparatus 100 directly transfers the toner image formed on the photoconductor 10 to the paper S.

FIG. 2 is a schematic view showing the peripheral structure of the secondary transfer device according to the embodiment. The peripheral structure of the secondary transfer device according to the embodiment will be described with reference to FIG.

As shown in FIG. 2, the secondary transfer device is composed of a secondary transfer roller 33 as a contact electrode and a drive roller 39 as a counter electrode. The secondary transfer roller 33 comes into contact with the recorded recording medium to be conveyed. The secondary transfer roller 33 functions as a contact electrode. The drive roller 39 is arranged to face the secondary transfer roller 33 so as to sandwich the recording medium.

The secondary transfer roller 33 and the drive roller 39 are composed of, for example, a core metal and a surface layer. The core metal is made of aluminum or iron and has a pipe shape. The surface layer is made of, for example, an ionic conductive rubber material. As the ionic conductive rubber material, for example, NBR (nitrile rubber), ECO (epichlorohydrin rubber) and the like can be blended and used. The drive roller 39 is rotationally driven by a drive source (not shown). Further, the intermediate transfer belt 30 is made of, for example, a polyimide film.

By applying a voltage between the secondary transfer roller 33 and the drive roller 39 in a state where the secondary transfer roller 33 and the drive roller 39 are sandwiched, the secondary transfer roller 33 and the drive roller 39 receive a primary current as a first current. Secondary transfer current flows.

This secondary transfer current flows more as the electrical resistance of the paper S is smaller. Further, the larger the capacitance of the paper S, the larger the secondary transfer current flows.

There are the following two paths through which the secondary transfer current flows. The first path is a path that passes through the transfer nip portion formed by the secondary transfer roller 33 and the drive roller 39. The second path is a path that passes through the gap formed between the secondary transfer roller 33 and the drive roller 39 on the upstream side and the downstream side of the transfer nip portion in the transport direction of the paper S.

The current flowing through the first path is the electric resistance on the first path (electrical resistance of each roller, electric resistance of paper S, electric resistance of the intermediate transfer belt 30) with respect to the transfer bias applied to the secondary transfer roller 33. It flows according to resistance). That is, the current flows according to Ohm's law. Therefore, the smaller the electric resistance of the paper S, the larger the current flows.

The current flowing through the second path flows due to the discharge. A voltage above a certain level (Paschen's law) is required to cause discharge in the voids, and the larger the capacitance of the paper, the smaller the potential loss on the paper. As a result, the potential difference in the void becomes large, and discharge is likely to occur. Therefore, the larger the capacitance of the paper, the larger the current flows.

FIG. 3 is a diagram showing the relationship between the secondary transfer current flowing through the secondary transfer device according to the embodiment and the electrical resistance of the paper. The relationship between the secondary transfer current flowing through the secondary transfer device and the electrical resistance of the paper will be described with reference to FIG.

FIG. 3 is detected by the first detection unit 71 when the electric resistances of the three types of paper S having thicknesses of 50 μm, 100 μm, and 150 μm are appropriately changed and each paper S is passed through the secondary transfer device. The secondary transfer current is shown.

The process speed when passing through the secondary transfer device is, for example, 100 mm / s, which is applied to the secondary transfer device (more specifically, between the secondary transfer roller 33 and the drive roller 39). The next transfer voltage is, for example, approximately 3000V. The thickness of the intermediate transfer belt 30 made of the polyimide film is, for example, 130 μm, and its volume resistance is approximately 1E3Ω. The thickness of the ionic conductive rubber used for the surface layer of the secondary transfer roller 33 is, for example, 3 mm, and its volume resistance is approximately 1E5Ω.

As shown in FIG. 3, in the region where the electric resistance of the paper S is low, the secondary transfer current changes according to the electric resistance. In the region where the electric resistance of the paper S is low, the current flowing through the secondary transfer nip portion becomes dominant.

Further, in a region where the electric resistance of the paper S is relatively low, a constant current flows regardless of the thickness of the paper S. In this case, the electric resistance of the paper S is low, and the electric resistance of the intermediate transfer belt 30 and the electric resistance of the secondary transfer roller 33 and the drive roller 39 are relatively large, so that these are dominant.

On the other hand, in the region where the electric resistance of the paper S is high, the secondary transfer current does not depend much on various electric resistances, but depends on the thickness of the paper S, that is, the capacitance.

When the width of the secondary transfer nip portion is 5 mm, the paper S passes through the secondary transfer nip portion in 1/20 second at the above process speed of 100 mm / s. Therefore, even if a bias of 3000 V, which is a secondary transfer voltage, is applied to the paper S, a current of 3 μA or less flows with an electric resistance of 1E9Ω or more. The current flowing in the region where the electric resistance of the paper S is high is rather dominated by the current due to electric discharge. Therefore, the secondary transfer current is greatly affected by the thickness of the paper, that is, the capacitance of the paper.

FIG. 4 is a diagram showing an example of each thickness of the paper and the electrical resistance of the paper when the secondary transfer current is 145 μA in the relationship shown in FIG. An example of the thickness of the paper and the electrical resistance of the paper when the secondary transfer current reaches a predetermined value will be described with reference to FIG.

Examples of the thickness of the paper (capacitance of the paper) and the electrical resistance of the paper when the secondary transfer current is 145 μA include three sets as shown in FIG. Therefore, it is difficult to accurately estimate the physical characteristics (capacitance and electrical resistance) of the paper by using only the secondary transfer current detected by the first detection unit 71.

Here, in the present embodiment, the static elimination current as the second current flowing through the static elimination electrode 62 can be detected by the second detection unit 72.

FIG. 5 is a schematic view showing the peripheral structure of the static elimination electrode according to the embodiment. The peripheral structure of the static elimination electrode according to the embodiment will be described with reference to FIG.

As shown in FIG. 5, the paper S that has passed through the secondary transfer nip portion formed between the secondary transfer roller 33 and the drive roller 39 is formed between the secondary transfer roller 33 and the drive roller 39 during the secondary transfer. It is charged by applying a high voltage between them.

The static eliminator current flowing from the charged paper S to the static eliminator electrode 62 by electric discharge depends on the amount of charge of the paper S and the capacitance of the paper. Since the amount of charge on the paper S due to charging is basically the amount of charge given by the secondary transfer, it depends on the amount of the secondary transfer current. That is, the amount of charge on the paper S due to charging depends on the electrical resistance and capacitance of the paper S.

Further, the amount of electric charge of the paper S due to charging is important until it reaches the static elimination electrode 62. Since the secondary transfer device 61 according to the embodiment is of the transfer roller type, charges of substantially the same amount and different polarities are applied to the front surface and the back surface of the paper in the secondary transfer nip portion.

Therefore, when the electric resistance of the paper S is low, the charges on the front surface and the back surface are neutralized between the time of the secondary transfer and the time when the paper S reaches the static elimination electrode 62, so that the static elimination current is reduced.

On the other hand, the static elimination electrode 62 is arranged on the back surface side of the paper S, and the discharge to the static elimination electrode 62 does not occur unless the potential difference between the back surface of the paper S and the static elimination electrode 62 becomes a potential of a predetermined value or more. The potential generated by the electric charge stored in the paper S depends on the electrostatic distance between the paper S and the static eliminating electrode 62.

As described above, since charges having different polarities exist on the front surface and the back surface of the paper S, a large potential difference is not generated when the electrostatic distances between the charges having different polarities are short. On the other hand, when the electrostatic distance between charges of different polarities on the paper is long, the potential difference becomes large. That is, the larger the electrostatic distance between the front surface and the back surface of the paper, that is, the smaller the capacitance of the paper, the larger the static electricity elimination current.

FIG. 6 is a diagram showing the relationship between the static elimination current flowing through the static elimination electrode according to the embodiment and the electrical resistance of the paper. With reference to FIG. 6, the relationship between the static elimination current flowing through the static elimination electrode and the electrical resistance of the paper according to the embodiment will be described.

In FIG. 6, the electrical resistances of the three types of paper S having thicknesses of 50 μm, 100 μm, and 150 μm are appropriately changed, and each paper S is passed through the secondary transfer device, and then flows from the paper S to the static elimination electrode 62. , The static elimination current detected by the second detection unit 72 is shown.

The process speed when passing through the secondary transfer device is, for example, 100 mm / s, which is applied to the secondary transfer device (more specifically, between the secondary transfer roller 33 and the drive roller 39). The next transfer voltage is, for example, approximately 3000V. The thickness of the intermediate transfer belt 30 made of the polyimide film is, for example, 130 μm, and its volume resistance is approximately 1E3Ω. The thickness of the ionic conductive rubber used for the surface layer of the secondary transfer roller 33 is, for example, 3 mm, and its volume resistance is approximately 1E5Ω.

Further, the static elimination electrode 62 has a saw blade shape and is connected to a ground electrode (GND). The distance between the static elimination electrode 62 and the paper S is approximately 0.1 mm. The static elimination electrode 62 is made of SUS.

As shown in FIG. 6, regarding the relationship between the electric resistance of the paper S and the static elimination current, when the horizontal axis is the electric resistance of the paper and the vertical axis is the static elimination current, the distribution of the electric resistance of the paper is convex having a peak. It is represented by a shape.

In the region where the electric resistance of the paper is 1E8Ω or less, the static elimination current sharply decreases as the electric resistance of the paper decreases, and becomes almost zero. In the region where the electric resistance of the paper is 1E8Ω or less, even if the current flowing through the paper S at the secondary transfer nip portion is large, the electric charge of the paper S is low and the charges are neutralized on the front surface and the back surface of the paper. Therefore, it becomes difficult to retain the electric charge by the time it reaches the static elimination electrode 62, and the static elimination current is reduced.

On the other hand, in the region where the electric resistance of the paper is 2E8 to 3E8Ω, the static elimination current has a peak, and in the region above that, the static elimination current decreases as the electric resistance of the paper increases. When the electrical resistance of the paper is high, the current flowing through the paper S at the secondary transfer nip portion becomes small, so that the static elimination current decreases.

Overall, the thicker the paper, that is, the smaller the capacitance, the larger the static electricity elimination current flows. This is due to the difference in electrostatic distance between the front surface and the back surface of the paper S as described above.

FIG. 7 is a diagram showing an example of the thickness of the paper and the electrical resistance of the paper specified from the secondary transfer current and the static elimination current.

As shown in FIG. 7, even when the secondary transfer current detected by the first detection unit 71 is approximately 145 μm, when the values of the static elimination current detected by the second detection unit 72 are different from each other. , Paper thickness, and paper electrical resistance are also different.

As described above, in the present embodiment, by detecting the secondary transfer current and the static electricity elimination current, the physical characteristics (capacitance and electrical resistance) of the paper that could not be specified only by detecting the secondary transfer current. ) Can be estimated accurately.

Strictly speaking, the value of the static elimination current has a peak with respect to the electrical resistance of the paper, so it is difficult to uniquely determine the physical characteristics of the paper unless it can be specified which side is before or after the peak. In some cases.

In this case, the paper S is conveyed again, a different secondary transfer voltage is applied between the secondary transfer roller 33 and the drive roller 39, and the secondary transfer current is detected by the first detection unit 71. The second detection unit 72 detects the static elimination current flowing from the paper S to the static elimination electrode 62 after applying different secondary transfer voltages.

In the region where the static elimination current decreases due to the low electrical resistance of the paper (on the left side (front side) of the peak), it is not easily affected by the secondary transfer voltage. On the other hand, in the region where the static elimination current decreases due to the high electrical resistance of the paper (on the right side (rear side) of the peak), increasing the secondary transfer voltage increases the static elimination current.

Therefore, by changing the secondary transfer voltage and detecting how the static elimination current changes, it is possible to determine which side the first measured static elimination current value is with respect to the peak. Can be done.

FIG. 8 is a diagram showing an example of a table used when calculating the physical characteristics of paper in the image forming apparatus according to the embodiment. An example of a table used when calculating the physical characteristics of paper will be described with reference to FIG.

As shown in FIG. 8, the storage unit (not shown) of the control unit 101 stores a table used for calculating the physical characteristics of the paper.

In the table, the secondary transfer voltage used at the time of detection, the thickness of the paper, the capacitance of the paper, the electric resistance of the paper, the secondary transfer current, and the static electricity elimination current are associated with each other. In the above table, as a combination of the secondary transfer voltage, the thickness of the paper, the capacitance of the paper, the electric resistance of the paper, the secondary transfer current, and the static eliminating current used at the time of detection, (V1, T1, Q1, R1) , TI1, RI1) to (Vn, Tn, Qn, Rn, TIN, RIn,) are stored. Note that n is a natural number.

Using the above table, the control unit 101 uses the above table to obtain the secondary transfer voltage used at the time of detection, the secondary transfer current detected by the first detection unit 71, and the static electricity elimination current detected by the second detection unit 72. The capacitance of the paper S and the electrical resistance of the paper S are estimated as the physical characteristics of the paper S.

The control unit 101 sets transfer conditions for transferring the toner image to the paper S based on the estimated capacitance of the paper S and the electrical resistance of the paper S.

The above table is created by conducting an experiment in advance by changing various conditions. Further, when the characteristics of the secondary transfer roller 33 and the intermediate transfer belt 30 change significantly depending on the environment such as temperature and humidity, it is preferable to create a plurality of tables corresponding to each environment. The above table may be corrected by using the VI characteristics of the secondary transfer voltage and the secondary transfer current in the secondary transfer device in the state where the paper S is not passed.

Further, the control unit 101 sets the cooling conditions of the cooling device 80 by using the secondary transfer current detected by the first detection unit 71 and the static elimination current detected by the second detection unit 72.

FIG. 9 is a schematic view showing a first state of the cooling device according to the embodiment. FIG. 10 is a schematic view showing a second state of the cooling device according to the embodiment. The cooling device 80 according to the embodiment will be described with reference to FIGS. 9 and 10.

As shown in FIGS. 9 and 10, the cooling device 80 is arranged on the downstream side of the fixing device 50 in the transport direction of the paper S. The cooling device 80 cools the paper S after the toner image transferred to the paper S is fixed.

The cooling device 80 includes a cooling unit 81 and a pressing mechanism 82. The cooling unit 81 has a cylindrical shape, and air blown from a cooling fan (not shown) passes through the inside of the cooling unit 81. The pressing mechanism 82 presses the cooling unit 81 toward the conveyed paper S.

As shown in FIG. 9, in the first state, the cooling unit 81 of the cooling device 80 is arranged apart from the transport path of the paper S. As shown in FIG. 10, in the second state, the cooling unit 81 of the cooling device 80 is pressed toward the paper S located on the transport path.

The paper S can be cooled by blowing air toward the inside of the cooling unit 81 using a cooling fan while the cooling unit 81 is pressed against the paper S.

The control unit 101 adjusts the amount of heat absorbed from the paper S by adjusting the cooling conditions such as the rotation speed of the cooling fan and the pressing condition.

By cooling the paper S after fixing, evaporation of water from the paper S can be suppressed. As a result, it is possible to suppress a decrease in the transferability of the second surface, particularly when a paper having a high electrical resistance is used. When paper having low electrical resistance is used, it is not necessary to cool the paper S, and the cooling device 80 does not have to be used.

Therefore, the control unit 101 determines the cooling conditions based on the secondary transfer current detected by the first detection unit 71 and the static elimination current detected by the second detection unit 72, thereby determining the cooling device 80. Wasted energy used for driving can be reduced.

More specifically, the control unit 101 estimates the electrical resistance of the paper using the detected secondary transfer current and static elimination current, and when the estimated electrical resistance of the recording medium is large, from the paper S by the cooling device 80. Increase the amount of heat absorption of.

The cooling device 80 may be composed of a cooling fan. In this case, the control unit 101 changes the amount of heat absorbed from the paper S by adjusting the rotation speed of the cooling fan and the like. Further, the cooling device 80 may be composed of a solid metal roller. In this case, the amount of heat absorbed from the paper S is changed by adjusting the pressing condition of the metal roller.

FIG. 11 shows the secondary transfer current and static elimination current measured by the first detection unit and the second detection unit according to the embodiment, the physical characteristics of the paper calculated from the secondary transfer current and the static elimination current, and the paper. It is a figure which shows an example of the transfer condition and the cooling condition determined from the physical property of.

An example of the secondary transfer current and static elimination current, the physical properties of the paper calculated from the secondary transfer current and static elimination current, and the transfer conditions and cooling conditions determined from the physical properties of the paper is as shown in FIG. ..

The control unit 101 associates, for example, the secondary transfer current and the static elimination current, the physical properties of the paper calculated from the secondary transfer current and the static elimination current, and the transfer conditions and the cooling conditions determined from the physical properties of the paper. The transfer conditions and cooling conditions are determined based on the detected secondary transfer current and static elimination current using the table.

In the case of paper having high electrical resistance, the formation of an electric field by applying an electric charge to the paper becomes dominant. Here, it is known that when the charge is not uniformly applied, creeping discharge occurs on the paper surface after passing through the transfer nip, and image noise is generated. This phenomenon can be suppressed by increasing the secondary transfer voltage to homogenize the charge applied to the paper.

Therefore, in the present embodiment, when the electric resistance of the paper is high as in 6.00E + 06, the control unit 101 increases the secondary transfer voltage to about 3300V to 4000V. Paper with a large electrical resistance has a large resistance to a relatively high voltage, so that there is no problem even if the secondary transfer voltage is increased.

On the other hand, when a relatively high voltage is set on a paper having a low electrical resistance such as 1.50E + 06, noise due to discharge in the paper is likely to occur, so that the secondary transfer voltage is 3000 V. It is preferable to lower the voltage to about 3300V.

When transferring to paper having a large electrical resistance, an electric field is formed in consideration of the size of the capacitance of the paper to some extent. Here, in the case of ordinary paper, the capacitance of the paper is affected by the moisture contained in the paper. Generally, in the fixing process using heat, moisture is lost due to the high temperature of the paper after fixing, and when the capacitance is lowered and the second surface is printed, transfer failure due to insufficient transfer electric field occurs. Prone.

Therefore, in the present embodiment, by cooling the paper using the cooling device 80 after fixing, it is possible to suppress the decrease in water content and the accompanying decrease in capacitance. In particular, when a paper having a high electric resistance such as 6.00E + 06 is used, the deterioration of the transferability of the second surface can be effectively suppressed by using the cooling device 80.

Even when paper with high electrical resistance is used, it is not necessary to cool the paper because the cooling effect of the paper cannot be expected for paper having a small capacitance such as 1.2E-07. .. In this case, it is preferable to reduce the process speed. On the other hand, in the case of paper having a low electric resistance such as 1.50E + 06, the paper S does not need to be cooled, and the cooling device 80 does not have to be used.

In this way, by adjusting the presence / absence of the cooling device 80 and the amount of heat absorption according to the physical properties of the paper, the wasted energy used to drive the cooling device 80 can be reduced.

When an electric field is formed by applying an electric charge to paper, there may be a restriction on the electric charge that can be applied only by a normal transfer process due to restrictions on the output upper limit of a high-voltage power supply or the like. In this case, the paper having high electrical resistance may be charged in advance before the normal transfer process is performed. The transfer quality can be improved by pre-charging the paper before performing the transfer process.

When the electrical resistance of the paper is medium as in 1.80E + 06 and the capacitance is small, it is possible to secure the magnitude of the transfer electric field by increasing the secondary transfer voltage. can. In this case, if there is a restriction on the output upper limit of the secondary transfer voltage, it is effective to suppress the process speed to, for example, about half. By suppressing the process speed, the time required for the paper to pass through the secondary transfer nip portion becomes longer, so that the amount of charge transfer within the paper increases, and as a result, the transfer electric field can be increased.

Since it is not very effective to slow down the process speed for paper having high electrical resistance, it is preferable to charge the paper in advance before performing the transfer process as described above.

FIG. 12 is a diagram showing a first example of a flow for determining transfer conditions in the image forming apparatus according to the embodiment. A first example of a flow for determining transfer conditions in the image forming apparatus 100 according to the embodiment will be described with reference to FIG.

The transfer conditions are determined when printing an image on the first sheet of paper or the first sheet of paper after changing the type of paper. The physical characteristic information of the paper (thickness of the paper and the capacitance of the paper) is stored for each cassette.

The first example is, for example, when the size of the paper contained in the cassette is A4, when printing the first sheet of paper, and at the beginning of the changed paper after the paper size is changed. This is a flow for determining transfer conditions when printing the first sheet.

As shown in FIG. 12, when determining the transfer conditions, the control unit 101 starts detecting the physical characteristics of the paper in step S10. Next, in step S20, the control unit 101 determines whether or not there is detection information detected by the first detection unit 71 and the second detection unit 72. Specifically, the control unit 101 determines whether or not the secondary transfer current and the static elimination current are detected. When it is determined that the secondary transfer current and the static elimination current are not detected (step S20: NO), the control unit 101 executes step S30. When it is determined that the secondary transfer current and the static elimination current are detected (step S20: YES), the control unit 101 executes step S110.

In step S30, the control unit 101 acquires paper information (paper width, thickness) and humidity information. The control unit 101 acquires paper information from the cassette information used, the contents set by the operation panel, and the like. The control unit 101 acquires humidity information from the hygrometer.

Next, in step S40, the control unit 101 tentatively determines a secondary transfer voltage that is generally considered to be appropriate, based on the paper information and humidity information acquired in step S30. At this time, the control unit 101 uses a table in which the relationship between the paper information and the humidity information and the secondary transfer voltage is preset.

Subsequently, in step S50, the control unit 101 gives an image output instruction. As a result, a toner image corresponding to the image to be output is formed by the image forming unit.

Next, in step S60, the control unit 101 passes the paper S from the cassette to the tray 48 along the transport path.

Subsequently, in step S70, the secondary transfer current is detected. Specifically, when the paper S passes through the secondary transfer nip unit, the secondary transfer current flowing through the secondary transfer device is detected by the first detection unit 71. The detected secondary transfer current is input to the control unit 101.

Next, in step S80, the static elimination current is detected. Specifically, the second detection unit 72 detects the static elimination current flowing from the charged paper S passing through the secondary transfer nip portion to the static elimination electrode 62. The detected static elimination current is input to the control unit 101.

Subsequently, in step S90, the control unit 101 estimates the physical characteristics of the paper (more specifically, the capacitance of the paper and the electrical resistance of the paper). At this time, as described above, the control unit 101 associates the secondary transfer voltage used at the time of detection, the thickness of the paper, the capacitance of the paper, the electrical resistance of the paper, the secondary transfer current, and the static eliminator current. The physical characteristics of the above paper are estimated with reference to the table.

If the table that can be referred to is inside, it may be complemented by performing interpolation processing or extrapolation processing from a nearby table.

Next, in step S100, the control unit 101 determines the secondary transfer voltage as the transfer condition. The control unit 101 determines the secondary transfer voltage based on the estimated capacitance of the paper and the electrical resistance of the paper. At this time, the control unit 101 may use the above table, or may use a preset calculation formula capable of determining the secondary transfer voltage from the capacitance of the paper and the electrical resistance of the paper.

Although step S100 has been described by way of example when it is performed after step S90, the present invention is not limited to this, and step S90 and step S100 may be performed at the same time.

When step S100 is completed, the process returns to step S10. When printing the second and subsequent sheets, it is determined in step S20 that there is detection information (step S20: YES). In this case, step S110 is carried out.

In step S110, the control unit 101 determines whether or not the cassette is opened or closed. When it is determined that the cassette is not opened / closed (step S110: NO), it is determined that the paper type has not been changed. In this case, step S170 is carried out and the secondary transfer voltage determined in step S100 is maintained.

When it is determined that the cassette is opened / closed (step S110: YES), it is determined that the paper type has been changed. In this case, step S120 is carried out.

In step S120, the control unit 101 acquires the information of the paper determined to be changed. Subsequently, in step S130, the control unit 101 determines whether or not the size is a predetermined size based on the acquired paper information. In this flow, it is determined whether or not the size of the acquired paper is A4. As for the paper information, similarly to the above, the paper information is acquired from the information of the cassette used, the contents set by the operation panel, and the like.

When it is determined that the size of the paper is a predetermined size (step S130: YES), it is determined that the type of paper has not been changed although the cassette has been opened and closed, and step S170 is performed. In step S170, as described above, the secondary transfer voltage determined in step S100 is maintained.

On the other hand, when it is determined that the size of the paper is not a predetermined size (step S130: NO), it is determined that the type of paper has been changed, and step S131 is carried out.

In step S131, the control unit 101 gives an image output instruction. As a result, a toner image corresponding to the image to be output is formed by the image forming unit.

Next, in step S140, the control unit 101 acquires detection information (secondary transfer current and static elimination current). Specifically, as in step S60, paper of different sizes is passed from the cassette toward the tray 48, and when the paper passes through the secondary transfer nip portion, the secondary transfer current flowing through the secondary transfer device is applied. It is detected by the first detection unit 71, and the static elimination current flowing from the charged paper S passing through the secondary transfer nip portion to the static elimination electrode 62 is detected by the second detection unit 72. The detected secondary transfer current and static elimination current are input to the control unit 101.

Subsequently, in step S150, the control unit 101 estimates the physical characteristics of the paper (more specifically, the capacitance of the paper and the electrical resistance of the paper). When the paper width is not A4, the amount of current flowing in the secondary transfer differs for each paper width. Therefore, the detected secondary transfer current is converted into a value corresponding to the width in the A4 horizontal direction by using a conversion table for each paper size set in advance. Since the static elimination current is proportional to the paper width, the detected static elimination current is converted into a value corresponding to the width in the A4 horizontal direction.

Based on the converted secondary transfer current value and static electricity elimination current value, the control unit 101 determines the secondary transfer voltage used at the time of detection, the paper thickness, the paper capacitance, and the paper, as described above. The physical properties of the above-mentioned paper are estimated by referring to the table in which the electric resistance, the secondary transfer current, and the static electricity elimination current are associated.

Next, in step S160, the control unit 101 determines the secondary transfer voltage as the transfer condition. The control unit 101 determines the secondary transfer voltage based on the estimated capacitance of the paper and the electrical resistance of the paper. At this time, the control unit 101 may use the above table, or may use a preset calculation formula capable of determining the secondary transfer voltage from the capacitance of the paper and the electrical resistance of the paper.

Although step S160 has been described by way of example when it is performed after step S150, the present invention is not limited to this, and step S150 and step S160 may be performed at the same time. Further, after step S160 or step 170 is performed, the process returns to step S10.

FIG. 13 is a diagram showing a second example of a flow for determining transfer conditions in the image forming apparatus according to the embodiment. A second example of a flow for determining transfer conditions in the image forming apparatus 100 according to the embodiment will be described with reference to FIG.

In the first example described above, the physical characteristics of the paper were estimated at the time of image printing, but in the second example of the flow for determining the transfer condition, the transfer condition changes the first sheet of paper or the type of paper. It is determined when the image is conveyed on the first first sheet of paper later without forming an image.

When the coverage of the paper is large, the secondary transfer current and the static elimination current are affected by the charging of the toner, so that it may not be possible to accurately estimate the physical characteristics of the paper depending on the coverage and humidity.

As in the second example, the physical characteristics of the paper can be accurately estimated by detecting the secondary transfer current and the static elimination current without forming an image.

Further, in the second example, the detected static elimination current is on either the front or the back of the peak of the distribution of the electric resistance of the paper when the horizontal axis is the electrical resistance of the paper and the vertical axis is the static elimination current. Contains a flow to identify.

As shown in FIG. 13, the second example of the flow for determining the transfer conditions is the step S40 for tentatively determining the secondary transfer voltage instead of the step S50 for instructing the image output when compared with the first example. From step S41 to the point where steps S41 to S43 are executed between step S60 through which the paper is passed, and between step S90 in which the physical characteristics of the paper are estimated and step S100 in which the secondary transfer voltage is determined, from step S91. The difference is that step S96 is performed.

In determining the transfer conditions, steps S10 to S40 are carried out in the same manner as in the first example.

Next, in step S41, the control unit 101 obtains print information (image information). By obtaining the print information (image information), the control unit 101 determines whether to perform double-sided printing or single-sided printing. Based on the print information of double-sided printing or single-sided printing, the method of passing paper is determined in step 60 described later.

Subsequently, in step S42, the control unit 101 determines whether or not the mode is in the non-image formation mode. If it is determined that the mode is the non-image formation mode (step S42: YES), step S60 is performed. On the other hand, when it is determined that the mode is not the non-image formation mode (step S42: NO), step S43 is performed.

In step S43, the non-image formation mode is set. For example, the user selects a non-image formation mode using an operation panel or the like.

Next, in step S60, the control unit 101 passes the paper S from the cassette to the tray 48 along the transport path. At this time, if it is determined in step S41 that double-sided printing is to be performed as described above, after the following steps S70 to S90 are performed, the double-sided path is passed so that an image can be formed. .. That is, the paper that has been passed through to determine the transfer conditions is passed through so that it can be reused at the time of image formation.

On the other hand, if it is determined in step S41 that single-sided printing is to be performed, the paper is passed so as to be ejected to the tray 48. That is, the paper that has been passed through to determine the transfer conditions is discharged to the tray 48. At this time, it is preferable to display an alarm for returning the paper discharged from the tray 48 to the cassette on a display unit such as an operation panel.

Subsequently, as in the first example, steps S70 to S90 are carried out. Step S91 is performed when or after the physical properties of the paper are estimated by step S90.

In step S91, the control unit 101 determines whether or not the detection information is insufficient.

When the static elimination current detected by the second detection unit 72 is a value near the peak with respect to the distribution of the electric resistance of the paper, the low resistance side and the high resistance side with respect to the peak are approximately the same. Since it is a value, it is necessary to determine whether it is located on the low resistance side or the high resistance side.

In this case, it becomes difficult to accurately estimate the physical characteristics of the paper only by the secondary transfer current detected by the first detection unit 71, and the control unit 101 determines that the detection information is insufficient. Specifically, for example, when the detected static elimination current is in the range of 80% or more of the peak value, the control unit 101 determines that the detection information is insufficient. On the other hand, when the detected static elimination current is a value different from the peak value, for example, when the detected static elimination current is smaller than 80% of the peak value, it is determined that the detection information is not insufficient. Will be done.

If it is determined that the detection information is not insufficient (step S91: NO), step S100 is executed.

If it is determined that the detection information is insufficient (step S92: YES), step S92 is executed. In step S92, the control unit 101 changes the secondary transfer voltage. For example, the control unit 101 raises the secondary transfer voltage by several hundred volts.

Next, in step S93, the control unit 101 passes the paper S from the cassette to the tray 48 along the transport path. As described above, when it is determined that double-sided printing is performed, the paper passed in step S60 is passed again. On the other hand, as described above, when it is determined that the printing is single-sided, the paper discharged to the tray 48 and returned to the cassette is passed through. If the paper ejected to the tray 48 has not been returned to the cassette, the next paper may be passed through.

Subsequently, in step S94, the secondary transfer current is detected. Specifically, when the paper S passes through the secondary transfer nip unit, the secondary transfer current flowing through the secondary transfer device is detected by the first detection unit 71. The detected secondary transfer current is input to the control unit 101.

Next, in step S95, the static elimination current is detected. Specifically, the second detection unit 72 detects the static elimination current flowing from the charged paper S passing through the secondary transfer nip portion to the static elimination electrode 62. The detected static elimination current is input to the control unit 101.

Subsequently, in step S96, the control unit 101 estimates the physical characteristics of the paper (more specifically, the capacitance of the paper and the electrical resistance of the paper).

When the secondary transfer voltage is changed, the area where the static elimination current decreases due to the low electrical resistance of the paper (on the left side (front side) of the peak) is less susceptible to the secondary transfer voltage, while the paper In the region where the static elimination current decreases due to high electrical resistance (on the right side (rear side) of the peak), increasing the secondary transfer voltage increases the static elimination current.

Therefore, by changing the secondary transfer voltage and detecting how the static elimination current changes, it is possible to determine which side the first measured static elimination current value is with respect to the peak. Can be done.

The control unit 101 performs the above-mentioned separation, and a table in which the secondary transfer voltage used at the time of detection, the thickness of the paper, the capacitance of the paper, the electrical resistance of the paper, the secondary transfer current, and the static electricity elimination current are associated with each other. Estimate the physical properties of the paper with reference to.

Next, in step S100, the control unit 101 determines the secondary transfer voltage as the transfer condition. The control unit 101 determines the secondary transfer voltage based on the estimated capacitance of the paper and the electrical resistance of the paper. At this time, the control unit 101 may use the above table, or may use a preset calculation formula capable of determining the secondary transfer voltage from the capacitance of the paper and the electrical resistance of the paper.

In the second example, when it is determined in step S91 that the detection information is not insufficient, only the first detection information (secondary transfer current and static elimination current detected at the first time) is used for the secondary. The case of determining the transfer voltage has been described as an example, but the present invention is not limited to this. It is first measured by measuring the secondary transfer current and static elimination current and detecting how the static elimination current changes when the image is formed by passing paper through the paper after determining the secondary transfer voltage. It may be possible to distinguish which side the value of the static elimination current is with respect to the peak. After performing the separation, the physical characteristics of the paper may be estimated, and the secondary transfer voltage may be determined as a transfer condition for subsequent printing.

FIG. 14 is a diagram showing a third example of a flow for determining transfer conditions and cooling conditions in the image forming apparatus according to the embodiment. A third example of a flow for determining odor transfer conditions and cooling conditions in the image forming apparatus 100 according to the embodiment will be described with reference to FIG.

In the second example described above, in the non-image formation mode, the transfer condition is determined by detecting the secondary transfer current and the static elimination current for determining the transfer condition, but the transfer condition and the cooling condition are determined. In the third example, in the image formation mode, the transfer condition is determined by detecting the secondary transfer current and the static elimination current for determining the transfer condition, and the cooling condition is determined.

As shown in FIG. 14, in the third example, when compared with the second example, steps S42A and S50 are carried out in place of steps S42 and S43, and step S180 is further carried out after step S100. Is different.

In the third example, steps S10 to S41 are carried out in the same manner as in the second example above when determining the transfer conditions and the cooling conditions.

Next, in step S42A, the control unit 101 determines whether or not to carry out from the first sheet. That is, the control unit 101 determines whether or not the image formation mode is used to form an image on the paper S.

If it is determined to be carried out from the first sheet (step S42A: YES), step S50 is carried out. In step S50, the control unit 101 gives an image output instruction. As a result, a toner image corresponding to the image to be output is formed by the image forming unit. Subsequently, as in the second example, step S60 and subsequent steps are carried out.

On the other hand, when it is determined not to carry out from the first sheet (step S42A: NO), it is determined that the transfer condition and the cooling condition are determined by the non-image formation mode. In this case, step S60 and subsequent steps are carried out in the same manner as in the second example.

After step S100 in which the secondary transfer voltage is determined is carried out, step S180 is carried out. Note that step S180 may be performed at the same time as step S100.

In step S180, the control unit 101 determines the rotation speed of the cooling fan as a cooling condition. Specifically, the control unit 101 estimates the electric resistance of the paper using the detected secondary transfer current and static elimination current, and when the estimated electric resistance of the paper is large, the cooling device 80 removes the electric resistance from the paper S. Increase the amount of heat absorption.

By cooling the paper S after fixing, evaporation of water from the paper S can be suppressed. As a result, it is possible to suppress a decrease in the transferability of the second surface, particularly when a paper having a high electrical resistance is used.

On the other hand, when the electric resistance of the paper is low, the control unit 101 determines that, for example, cooling of the paper S is unnecessary, reduces the rotation speed of the cooling fan, or stops the cooling fan. As a result, power consumption can be reduced.

FIG. 15 shows the physical characteristics and transfer conditions of the paper based on the secondary transfer current and static elimination current detected by the first detection unit and the second detection unit according to the embodiment and the detected secondary transfer current and static elimination current. It is a figure which shows an example of the table used when determining a cooling condition.

As described above, when determining the number of rotations of the cooling fan as the cooling condition in step S180, for example, as shown in FIG. 15, the detected secondary transfer current, static elimination current, and paper capacitance are used. A table in which the electric resistance of the paper, the secondary transfer voltage as the transfer condition, and the cooling fan rotation speed as the cooling condition are associated with each other is used.

Even if the detected secondary transfer current is a predetermined value (same value), the control unit 101 appropriately sets the cooling fan rotation speed according to the detected static elimination current. Further, the control unit 101 appropriately sets the cooling rotation speed according to the detected secondary transfer current even if the detected static elimination current is a predetermined value (same value). As a result, the cooling conditions can be set appropriately.

FIG. 16 is a diagram showing a fourth example of a flow for determining transfer conditions and cooling conditions in the image forming apparatus according to the embodiment. A fourth example of a flow for determining transfer conditions and cooling conditions in the image forming apparatus 100 according to the embodiment will be described with reference to FIG.

In the fourth example of the flow for determining the transfer condition and the cooling condition, the static elimination current detected in step S95 after changing the secondary transfer voltage in step S92 and the secondary transfer voltage change are compared with the third example. The difference is mainly in that when an abnormality is detected, the abnormality is notified by comparing with the static elimination current detected in step S80 before.

The secondary transfer current can be automatically corrected according to the environment and roller resistance by applying a bias when no paper is passed. Therefore, if there is an abnormality in the secondary transfer current, it can be detected at the time of this correction.

On the other hand, regarding the static elimination current, it is not possible to detect an abnormality in the non-passing state. Further, if the physical characteristics of the paper are not known, it is difficult to detect an abnormality only by the measured static elimination current even at the time of passing the paper. When the electrical resistance of the paper is low, it is difficult for the static elimination current to flow, so it may not be possible to distinguish whether it is flowing due to an abnormality or whether the paper resistance is low and it is not flowing. Examples of the abnormality related to the static elimination current include poor continuity due to paper dust and foreign matter.

In the present embodiment, since the physical characteristics of the paper are estimated using both the detected secondary transfer current and the static elimination current, if an abnormality related to the static elimination current occurs, the paper is erroneously used. There is a possibility of estimating the physical properties of. Therefore, in the fourth example, as described above, the flow is such that an abnormality related to the static elimination current can be detected.

Specifically, in the fourth example, the static elimination current detected by the second detection unit 72 when the higher voltage of the secondary transfer voltages applied before and after the change is applied is different from each other. When the lower voltage of the transfer voltage is applied and the current is not larger than the static elimination current detected by the second detection unit 72, the notification unit provided in the image forming apparatus notifies the abnormality.

Further, in the fourth example, when an abnormality is notified by the notification unit, the image formation process is stopped or the secondary transfer voltage is set using only the secondary transfer current detected by the first detection unit 71. do.

As shown in FIG. 16, the fourth example differs from the third example in that steps S191 to S193 are carried out.

In the fourth example, steps S10 to S96 are carried out in the same manner as in the third example above when determining the transfer conditions and the cooling conditions.

When step S96 is carried out, step S190 is carried out. In step S190, the control unit 101 determines whether or not an abnormality related to the static elimination current has occurred. Specifically, the control unit 101 is detected by the second detection unit 72 when a higher of the different secondary transfer voltages applied between the secondary transfer roller 33 and the drive roller 39 is applied. It is determined whether the static elimination current is larger than the static elimination current detected by the second detection unit 72 when the lower of the secondary transfer voltages different from each other is applied.

When the static elimination current detected when the higher of the secondary transfer voltages different from each other is applied is larger than the static elimination current detected when the lower voltage of the secondary transfer voltages different from each other is applied. It is judged that no abnormality has occurred.

On the other hand, the static elimination current detected when the higher of the secondary transfer voltages different from each other is applied is larger than the static elimination current detected when the lower voltage of the secondary transfer voltages different from each other is applied. If it is not large, it is judged that an abnormality has occurred.

If it is determined that no abnormality related to the static elimination current has occurred (step S190: NO), step S100 is performed.

On the other hand, when it is determined that an abnormality related to the static elimination current has occurred (step S190: YES), step S191 is executed.

In step S191, the notification unit notifies an abnormality related to the static elimination current. Specifically, the abnormality is displayed on the display panel or the like, or the maintenance service company or the like is notified of the abnormality by using wired or wireless communication.

Next, in step S192, the secondary transfer voltage is tentatively determined by using only the value of the secondary transfer current detected by the first detection unit 71 without using the value of the detected static elimination current. .. Subsequently, in step S193, the rotation speed of the cooling fan is tentatively determined.

In addition, step S192 and step S193 may be carried out at the same time, and steps S191, step S192, and step S193 may be carried out at the same time.

As described above, in the image forming apparatus according to the present embodiment, the toner is used by using the secondary transfer current detected by the first detection unit 71 and the static elimination current detected by the second detection unit 72. By setting the transfer conditions for transferring the image to the recording medium, it is possible to set the transfer conditions more accurately than when the transfer conditions are set by detecting either the secondary transfer current or the static elimination current. can.

In addition, when setting the transfer conditions, the detected secondary transfer current and static elimination current are used to estimate the electrical resistance and capacitance of the paper, and based on the estimated electrical resistance and capacitance of the paper. By setting the transfer conditions, it is possible to accurately set the transfer conditions that are difficult to uniquely determine either the electrical resistance or the capacitance of the paper.

In the present embodiment, a first electrode portion including a contact electrode that contacts the conveyed paper and a counter electrode that is arranged to face the contact electrode so as to sandwich the conveyed paper is formed by a secondary transfer device. Although the case where it is configured has been described as an example, the present invention is not limited to this.

As long as the contact electrode and the counter electrode are configured so that a voltage can be applied to the contact electrode and the counter electrode while the paper is sandwiched between the contact electrode and the counter electrode, the contact electrode and the counter electrode may be formed in a plate shape or in a roller shape. It may be formed. In this case, the contact electrode and the counter electrode may be arranged on the upstream side of the secondary transfer device or on the downstream side of the secondary transfer device in the paper transport direction.

When the first electrode portion is configured by the secondary transfer device as described above, the number of parts can be reduced.

The case where the second electrode portion arranged in a non-contact manner on the paper so as to be movable so that the electric charge charged on the paper is configured by the static elimination electrode has been described as an example, but the present invention is not limited to this. It can be changed as appropriate within the range that does not deviate from the purpose.

As described above, the embodiment invented this time is an example in all respects and is not limiting. The scope of the present invention is indicated by the claims and includes all modifications within the meaning and scope equivalent to the claims.

1C, 1K, 1M, 1Y image forming unit, 10 photoconductor, 11 charging device, 12 exposure device, 13 developing device, 14 developing roller, 15C, 15K, 15M, 15Y toner bottle, 17 cleaning device, 30 intermediate transfer belt, 31 Primary transfer roller, 33 Secondary transfer roller, 37 Cassette, 38 Driven roller, 39 Drive roller, 40 Timing roller, 41 Conveyance path, 48 trays, 50 Fixing device, 61 Secondary transfer device, 62 Static elimination electrode, 71 First Detection unit, 72 2nd detection unit, 80 cooling device, 81 cooling unit, 82 pressing mechanism, 90 housing, 100 image forming device, 101 control unit.

Claims (15)

It is an image forming device
A first electrode portion including a contact electrode that contacts the recorded recording medium to be transported and a counter electrode that is arranged to face the contact electrode so as to sandwich the recorded recording medium to be transported.
A second electrode portion that is arranged in a non-contact manner with respect to the recording medium so that the electric charge charged on the recording medium can move.
A first detection unit that detects a first current flowing through the first electrode unit by applying a voltage between the contact electrode and the counter electrode while the recording medium is sandwiched between the contact electrode and the counter electrode.
A second detection unit that detects the second current flowing from the charged recording medium to the second electrode unit, and
The first detection unit and the control unit for inputting the detection results of the second detection unit are provided.
The control unit uses a table in which the first current, the second current, and the electric resistance and capacitance of the recording medium are previously associated with the first current detected by the first detection unit. The electric resistance and capacitance of the recording medium are estimated using the second current detected by the second detection unit, and the transfer conditions are set based on the estimated electric resistance and capacitance of the recording medium. , Image forming device. The image forming apparatus according to claim 1, wherein the first electrode portion is composed of a transfer device that transfers a toner image carried on a toner image carrier to a recording medium. The image forming apparatus according to claim 1 or 2 , wherein the second electrode portion is composed of a static elimination electrode that removes electric charges charged in the recording medium. The image forming apparatus according to any one of claims 1 to 3 , wherein the second electrode portion is arranged on the downstream side of the first electrode portion in the transport direction of the recording medium. When the relationship between the electrical resistance of the recording medium and the second current is such that the horizontal axis is the electrical resistance of the recording medium and the vertical axis is the second current, the distribution of the electrical resistance of the recording medium is convex with a peak. Represented by shape,
When the detected second current is a value located in the region before and after the peak, the control unit applies a different voltage between the contact electrode and the counter electrode to apply a different voltage to the first detection unit. The transfer condition is set using the first current detected by the first current and the second current that flows from the recording medium to the second electrode section after applying a different voltage and is detected by the second detection section. The image forming apparatus according to claim 4. The second current detected by the second detection unit when a higher voltage among the different voltages applied between the contact electrode and the counter electrode is applied is applied to the first electrode unit. The fifth aspect of claim 5, further comprising a notification unit that notifies an abnormality when the lower voltage of the different voltages is applied and the current is not larger than the second current detected by the second detection unit. Image forming device. When an abnormality is notified by the notification unit, the control unit stops the image forming process or sets the transfer condition using only the first current detected by the first detection unit. The image forming apparatus according to claim 6. The control unit and the first current detected by the first detection unit when printing on the first recording medium or the first recording medium after changing the type of the recording medium. The image forming apparatus according to any one of claims 1 to 7 , wherein the transfer condition is set by using the second current detected by the second detection unit. The control unit is detected by the first detection unit when the first first recording medium or the type of the recording medium is conveyed to the first first recording medium after the change without forming an image. The image forming apparatus according to any one of claims 1 to 7 , wherein the transfer conditions are set by using the first current and the second current detected by the second detection unit. The control unit estimates the electrical resistance and capacitance of the recording medium using the detected first current and the detected second current, and when the estimated electrical resistance of the recording medium is large. Claims 1 to 9 , wherein the transfer voltage applied to the transfer device when transferring the toner image from the toner image carrier to the recording medium is increased, and when the capacitance of the recording medium is large, the transfer voltage is decreased. The image forming apparatus according to any one item. Further provided with a cooling device for cooling the recording medium after the toner image transferred to the recording medium is fixed.
The control unit sets the cooling conditions of the cooling device by using the first current detected by the first detection unit and the second current detected by the second detection unit. 10. The image forming apparatus according to any one of 10. The control unit estimates the electrical resistance of the recording medium using the detected first current and the detected second current, and when the estimated electrical resistance of the recording medium is large, the cooling device is used. The image forming apparatus according to claim 11 , wherein the amount of heat absorbed from the recording medium is increased. It is an image forming device
A first electrode portion including a contact electrode that contacts the recorded recording medium to be transported and a counter electrode that is arranged to face the contact electrode so as to sandwich the recorded recording medium to be transported.
A second electrode portion that is arranged in a non-contact manner with respect to the recording medium so that the electric charge charged on the recording medium can move.
A first detection unit that detects a first current flowing through the first electrode unit by applying a voltage between the contact electrode and the counter electrode while the recording medium is sandwiched between the contact electrode and the counter electrode.
A second detection unit that detects the second current flowing from the charged recording medium to the second electrode unit, and
The first detection unit and the control unit for inputting the detection results of the second detection unit are provided.
The control unit sets transfer conditions for transferring the toner image to the recording medium using the first current detected by the first detection unit and the second current detected by the second detection unit. ,
The second electrode portion is arranged on the downstream side of the first electrode portion in the transport direction of the recording medium.
When the relationship between the electrical resistance of the recording medium and the second current is such that the horizontal axis is the electrical resistance of the recording medium and the vertical axis is the second current, the distribution of the electrical resistance of the recording medium is convex with a peak. Represented by shape,
When the detected second current is a value located in the region before and after the peak, the control unit applies a different voltage between the contact electrode and the counter electrode to apply a different voltage to the first detection unit. The transfer condition is set using the first current detected by the first current and the second current that flows from the recording medium to the second electrode section after applying a different voltage and is detected by the second detection section. Image forming device. The second current detected by the second detection unit when a higher voltage among the different voltages applied between the contact electrode and the counter electrode is applied is applied to the first electrode unit. The thirteenth aspect of the present invention, further comprising a notification unit for notifying an abnormality when the lower voltage of the different voltages is applied and the current is not larger than the second current detected by the second detection unit. Image forming device. When an abnormality is notified by the notification unit, the control unit stops the image forming process or sets the transfer condition using only the first current detected by the first detection unit. The image forming apparatus according to claim 14.

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